Torkham border crossing remains closed for the fourth day as violence over construction of a gate by Pakistan continues.

At least one Afghan border guard has been killed in renewed clashes at a Pakistani-Afghan border crossing, according to an Afghan official.

Wednesday's death was the third since Sunday night, when the violence erupted at the Torkham border crossing over the construction of a gate by Pakistan on allegedly disputed territory.

More than two dozen border guards from both sides have been wounded so far in the shootouts.

"When our people began construction work on the gate on Wednesday, Afghan forces again opened fire at our troops and construction workers," said a Pakistani security official who declined to be identified.

He said Pakistan had retaliated with long-range artillery and mortars.

Afghan officials, however, denied any fighting on Wednesday, but said an Afghan border guard was killed and five were wounded overnight on Tuesday. It was not immediately clear if the officials were talking about the same incident.

Pakistan said the border gate it was building was well on its side of the border and would help to stop armed fighters from crossing and help to fight drug trafficking.

Afghanistan objected to all Pakistani construction on a 2,200-km border that it said was unfairly imposed by British colonialists in the 19th century and which it had never recognised.

Relations between Pakistan and Afghanistan have been particularly strained in recent months over Afghan officials' anger at what they see as insincere efforts by Pakistan to help with peace talks between the Afghan government and the Taliban.